1. Field of the Invention
The present invention relates to measuring instruments, and particularly to a cylindrical ruler for easily and accurately measuring curved objects (such as cylindrical lenses, pipes and hoses) and drawing and/or etching thereon.
2. Description of the Related Art
Cylindrical objects, such as cylindrical lenses, are difficult to measure accurately with normal measuring instruments. Typically, a tape ruler would be used, but this practice can be subject to wide variances and inaccuracies due to the inherent flexibility and/elasticity of tape rulers, as well as potential human error.
Many measuring devices have been proposed that may facilitate measuring of circular objects. A common measuring instrument is a bow compass. Some accurate measurements can be obtained, but a bow compass must be matched against a separate ruler, often repeatedly, in order to obtain such results.
Another instrument that is commonly used is a protractor. Depending on the gradients used, these can provide very accurate measurements in degrees, radians, and in some designs, the actual arc length or diameter. However, common protractors tend to be very limited in measuring arcs or diameters, since the diameter of the object and the diameter of the protractor must be the same for accurate results. Otherwise, additional conversions and calculations must be made to obtain the desired results.
Still another conventional instrument includes a mandrel, such as a jeweler's mandrel. These instruments are usually constructed as an elongate, frustoconical bar having a handle at one end. The elongate bar is usually marked along the length thereof with standard ring sizes, so that the size or inner diameter of a ring can be easily determined by sliding the ring on the bar. Wherever the ring stops, the corresponding size is indicated by a mark next to the ring. This type of instrument is accurate to a degree, but limited to the size of the mandrel and the structure thereof, which usually renders the mandrel applicable to relatively small diameter structures. Moreover, if the user desires to draw with a mandrel-type instrument, the drawing would be limited to the circle at the end of the mandrel. The mandrel also lacks a straight edge for a user to use in order to generate a straight line.
In light of the above, it would be a benefit in the art of measuring instruments to provide a device that can accurately measure a variety of circular objects in a relatively fast manner and facilitate drawing thereof. Thus, a cylindrical ruler solving the aforementioned problems is desired.